Ch.1 · Unit 5

Equilibrium — one number for the whole thing

"What temperature is it?" only has an answer once everything has stopped disagreeing with everything else. Until then, the honest answer is no single number.

TEA
ROOM
SPOON
ICE
SAND
PISTON
Just-poured tea
Bottom scalding, top drinkable. Tap to wait and watch the bands argue their way to one answer.
— °C
NO SINGLE ANSWER YET
TAP TO WAIT
Ask "what temperature is this tea?" right now — there genuinely isn't one number that's true everywhere in the cup.
A room, AC just switched on
Corners disagree with the middle. Tap to wait.
❄️
— °C
NO SINGLE ANSWER YET
TAP TO WAIT
Every corner of this room would show a different reading on a thermometer right now.
A metal spoon in hot soup
The submerged end is already hot. The handle hasn't heard the news. Tap to wait.
— °C
NO SINGLE ANSWER YET
tip (in soup)handle
TAP TO WAIT
Metal conducts fast, but not instantly. For a few minutes, "the spoon's temperature" isn't a real question.
Ice floating in water
Genuinely 0 °C throughout — but only once it settles. Tap to wait.
🧊
−6 °C
ice
💧
18 °C
water
TWO DIFFERENT ANSWERS RIGHT NOW
TAP TO WAIT
Both readings will land on exactly the same number — and it isn't the average of −6 and 18.
A shaken bottle of sand
Shake it, then let it settle. Only one of those states can be described in a word.
SHAKE IT UP
Shaken, the surface is chaos — no single "sand level" means anything. Settled, one word does the whole job: flat.
Push the piston — slowly, then fast
Drag the piston down. Go gently, then try a fast shove.
100 kPa
GAS AT REST
Slow enough, and the gas is uniform at every instant — one pressure describes it the whole way. Push it fast and that stops being true, even for a moment.
Puzzle · The Refusing Thermometer
An uneven metal plate
A blowtorch hits one corner of this plate. Tap the torch, then try reading the thermometer whenever you like. It will refuse until it's honest to do otherwise.
— °C
🔥 APPLY TORCH
📏 READ IT NOW

That refusal wasn't a bug — it was the correct answer. A single temperature is only ever meaningful for a system in equilibrium. Everywhere in Chapters 2 onward that a problem says "the gas is at temperature T," it's quietly promising you this state first.